In certain prior art communication networks, data is transferred between elements (“network elements”) in the form of frames in accordance with an interface for an optical network, such as “Network Node Interface for Optical Transport Network (OTN)” as defined in the ITU-T Recommendation G.709. One such prior art frame 10 (illustrated in FIG. 1A) has four rows 11-14. Each of rows 11-14 has an overhead bytes (e.g. 16 bytes), payload bytes (e.g. 3808 bytes) and error correction bytes (e.g. 256 bytes).
Typically, the error correction bytes are prepared by a well-known scheme, such as a Reed-Solomon (RS) code, wherein 16 bytes of parity are added for every 239 bytes of data. Such an OTN row 11 may be stored or prepared, and transmitted sequentially by columns in a two-dimensional array. For example, as illustrated in FIG. 1B, initial bytes 1-16 are stored in a column 15, followed by bytes 17-32 being stored in column 16, and so on. The bytes of OTN row 11 are supplied sequentially by array rows, to an FEC encoder/decoder. For example, in the array shown in FIG. 1B, a data group 22 in the top-most row 21 has 239 bytes and these bytes are encoded/decoded using 16 bytes in parity group 23 also located in top-most array row 21.
The above-described method for transmission/receipt by columns and encoding/decoding by rows may be accomplished by use of an interleaver of the type described in U.S. Pat. No. 4,559,625 granted to Berlekamp et al, entitled “Interleavers for digital communications” incorporated by reference herein in its entirety as background. As stated therein, it is well known in the art to interleave block codes to exploit helical symmetry, in data that is transmitted and received in a communications network. However, such a prior art helical interleaver with single level coding is too inefficient for modern communications. Here, by single level coding we mean that every bit is protected by a single codeword or equivalently every bit belongs to only one codeword. Hence, the inventors believe an improved interleaving and corresponding encoding/decoding circuit and method is needed, as described below.